FIG. 7 is an example of a high-frequency circuit device of the prior art which employs a multiple-layer board 11 comprising a wiring layer 11a on the top face, a grounding layer 11d on the bottom face, a grounding layer 11b provided on an insulating material inside the multiple-layer board 11, and a wiring layer 11c provided on an insulating material between the grounding layers 11b and 11d. A line 12, or trace, is disposed on the surface of the multiple-layer board 11, and a line 13 crosses line 12 on the same surface as line 12. Line 13 has an unconnected section 13x (indicated with the broken line) which is not electrically connected at the crossing area. A line 14 is disposed on wiring layer 11c at an area which crosses underneath line 12. Both ends of line 13 facing the unconnected section 13x are electrically connected with line 14 respectively using through-holes 15a and 15b. A high-frequency circuit device of the prior art as explained above may require the entire board to be designed in multiple layers the crossing area being just a part of the overall wiring on the board.
In the above structure, one disadvantage is that a multiple layer board may be required if even only one crossing of signal lines exists in the circuit, resulting in higher component cost.
Another disadvantage is that the characteristic impedance of signal lines on the wiring layers 11a and 11c becomes smaller compared to that of a board with the same thickness which does not have multiple layers because of the presence of the grounding layers 11b and 11d. To obtain the equivalent characteristic impedance of signal lines to that of a board which does not have multiple layers, lines may need to be made thinner, resulting in increased resistance of lines, thereby causing deterioration in characteristics due to transmission loss.
Simple jumper chips have already been implemented for crossing lines on a board. However, jumper chips may cause electrical coupling between lines, resulting in deterioration of performance.